Systematic investigation of CO 2  : NH 3 ice mixtures using mid-IR and VUV spectroscopy - part 1: thermal processing.

The adjustment of experimental parameters in interstellar ice analogues can have profound effects on molecular synthesis within an ice system. We demonstrated this by systematically investigating the stoichiometric mixing ratios of CO 2  : NH 3 ices as a function of thermal processing using mid-IR and VUV spectroscopy. We observed that the type of CO 2 bonding environment was dependent on the different stoichiometric mixing ratios and that this pre-determined the NH 3 crystallite structure after phase change. The thermal reactivity of the ices was linked to the different chemical and physical properties of the stoichiometric ratios. Our results provide new details into the chemical and physical properties of the different stoichiometric CO 2  : NH 3 ices enhancing our understanding of the thermally induced molecular synthesis within this ice system.